gmc 350 truck tbi 350 wont start

had 1995 gmc truck under water. replaced computer, disributor, fuel pump assembly.i had no compression, so i swapped the block and heads from a 1992 chevrolet. it had a 4 brl carb and intake, but i kept my throttle body and intake... i have good fuel spray and clean fuel, i have fire at all plugs ( used a spark checker ), and with engine at tdc on #1, the rotor button faces the #1 plug on compression stroke. will not start.

it started a couple of times but i had done something really stupid i had the engine block grounded, but not the neg side of battery. then engine block ground burned in to, so i replaced it with 6 gauge wire. since the ground burned, it turns over and almost cranks, but wont... Please help!